What is the regex for base64 string (strict)?

The regex pattern for base64 string (strict) is `^[A-Za-z0-9+/]{4,}(?:={0,2})$`. This pattern validates strict base64 encoded string (min 4 chars, proper padding).

How do I use this regex in JavaScript?

In JavaScript, create the regex with `const regex = /^[A-Za-z0-9+\/]{4,}(?:={0,2})$/;` and test with `regex.test(yourValue)`. It returns `true` if the value matches.

How do I use this regex in Python?

In Python, use `import re; re.match(r'^[A-Za-z0-9+/]{4,}(?:={0,2})$', value)`. The raw string prefix (`r`) prevents Python from interpreting backslashes as escape characters.

Is this regex case-sensitive?

By default, yes. To make it case-insensitive, add the `i` flag in JavaScript (`/^[A-Za-z0-9+/]{4,}(?:={0,2})$/i`) or use `re.IGNORECASE` in Python.

Regex for Base64 String (Strict)

Regex Pattern

^[A-Za-z0-9+/]{4,}(?:={0,2})$

Strict base64 encoded string (min 4 chars, proper padding)

Quick Answer

The regex pattern for base64 string (strict) is `^[A-Za-z0-9+/]{4,}(?:={0,2})$`. Strict base64 encoded string (min 4 chars, proper padding). This works in JavaScript, Python, Ruby, PHP, Java, and most regex engines that support PCRE syntax.

Test Examples

Input	Result
SGVsbG8=	✓ Matches
dGVzdA==	✓ Matches
YWJjZGVmZw==	✓ Matches
abc	✗ No match
not*base64!	✗ No match
===	✗ No match

Code Examples

javascript

const regex = /^[A-Za-z0-9+\/]{4,}(?:={0,2})$/;
const isValid = regex.test(value);

python

import re
pattern = r'^[A-Za-z0-9+/]{4,}(?:={0,2})$'
if re.match(pattern, value):
    print("valid")

ruby

pattern = /^[A-Za-z0-9+/]{4,}(?:={0,2})$/
if value =~ pattern
  puts "valid"
end

php

if (preg_match('/^[A-Za-z0-9+\/]{4,}(?:={0,2})$/', $value)) {
    echo "valid";
}

java

String pattern = "^[A-Za-z0-9+/]{4,}(?:={0,2})$";
boolean isValid = value.matches(pattern);

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